Tense shoulders
This is a complaint that most people have. After sitting behind the screen, our shoulders get tense. I myself find the combination of not sitting up straight and carrying a heavy rucksack (containing laptop, power adapter, network cable, laptop lock, extra network card, bag of cdroms, lunchbox, pile of papers, book to read, you name it) detrimental. Because of the weight of the bag, I tend to hunch and use force in my shoulders. Also when my desk, chair and screen aren't well aligned, I tend to hunch.
Hunching is a bad thingTM. Our lungs do not get enough space, so our breathing becomes shallow, which does not help us to relax. Other organs also get less room.
Now that we know this, we know how to prevent it: simply try not to hunch. But what if we have hunched too much already? There are a few exercises that may help. In fact there are lots of exercises and you have probably already discovered what movements feel good. Let's try a few:
Yawning
This exercise is simple, as most of us can already do it. The difference is this time, that we should involve our whole body into the yawn. When you yawn, stretch your arms up and backward as far as possible. You should feel a nice stretching feeling in your arms and shoulders. Be careful however if the tension is really bad, don't overdo it!
Breathe in as far as you can and if you want, even hold your breath for a few seconds before you breathe out. When you breathe out, let go of all tension in your arms and shoulders. This will also give you more oxygen.
Rotating the shoulders
You will notice that rotating the shoulders is a great way to make them more flexible. You will also notice that you were more tense than you thought you were. You can do this by yourself or have someone rotate your shoulders for you.
DIY
This exercise (called "hands turn double wheel") comes from the sitting eight pieces of brocade, a set of chinese stretching exercises. You can find references to this set if you search for "ba duann gin" (chinese name) or "hachi dan kin" (japanese name). There are many variants on these exercises and it is hard to say which one is the authentic and original. Then again, when it does the job, why should you care? A nice book is "The Eight Pieces of Broccade" by Jang Jwing Ming.
Here's how to do it: Sit flat on your buttocks with your legs and feet comfortably stretched out in front of you. Face forward and lift up your arms, so that your palms face down. Now start making circles with your shoulders and elbows, as if you were one of those ancient steam locomotives. Keep your hands flat! I noticed that with a lot of chinese exercises, the number of repetitions is quite high, but you will sure feel the effect! After say, 36 repetitions, move your shoulders in the other direction.
Let someone do it
You can do this when a person sits on a chair. Stand next to the person and let his/her arm rest on your arm, while gently holding the wrist. It works best if you use the same side arm as the side you are trying to loosen up, e.g. you take the left arm with your left arm. Place the other arm on the shoulder to keep it in place.
Now gently make the same circular motions as described in the previous exercise. The person undergoing this movement (sometimes known as 'the victim' ;-) ) should totally relax and let the other person do the movement. Most people tend to automatically move along. If this happens, slow down or stop the movement and remind the person to relax. When he/she relaxes, continue. In order to give good support for the arm, you should take a wide stance and shift your body weight from one foot to the other. This way you will not get tired. In the picture (thanks to gvinevere for posing) you can see this a bit clearer (read left to right).
After you have done this for a while, treat the other shoulder. Which one you do first is up to you. Some people treat the tenser shoulder first, other people treat the looser shoulder first. A tense muscle tends to become more tense if the person cannot relax or if the movement is uncomfortable. When you notice this, you may want to treat the other shoulder first and come back to this one later.
You can also rotate the arm while it is stretched. This way you'll make a bigger circle and the shoulder is rotated in a different way.
Shrugging
Shrugging is one of those other things we all do, but who cares? Well, shrugging, when done right, can help your shoulders relax. Here's how to shrug:
Lift your shoulders while breathing in and then suddenly let the shoulders drop. Do this a few times.
You can also do each shoulder individually and if you alternate both shoulders, you may make a very good impression on the dancefloor.
When doing these exercises, you should become aware of where the tension in your shoulders is. After a while you can notice what is causing the tension in your shoulders. It could be bad posture, stress at work (e.g. deadlines), unhappiness about something, an injury or whatever. Once you know that, you can deal with the cause. In the meantime, the exercises may help.